Dynamical calculation of magnetization reversal in elongated particles

The Landau–Lifshitz–Gilbert (LLG) equation is directly solved to investigate squareness and time-dependent magnetization changes of elongated particles. Squareness scarcely changes until the particle size exceeds some critical value. The critical value increases with increasing aspect ratio. It was found that there are three kinds of magnetization reversal mechanism in elongated particles: flower1, flower2, and vortex particles. Some time interval is necessary for the irreversible transition to occur in all cases. In a flower1 particle, the transition occurs from the top and bottom planes. In flower2 and vortex particles, the irreversible transitions occur from vortex states. In a flower2 particle, during the irreversible transition process, all magnetic moments at the top and bottom planes rotate to the same direction; consequently, some magnetic moments rotate to the antiapplied-field direction and then rotate to the applied-field direction. In a vortex particle, each magnetic moment at the top and bottom planes rotates to the applied-field direction.